<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <script>
      // indexOf
      var arr = [1, 2, 3, 3, 4, 5, 1, 2]
      function unique(arr) {
        let newArr = []
        for (let i = 0; i < arr.length; i++) {
          if (newArr.indexOf(arr[i]) === -1) {
            newArr.push(arr[i])
          }
        }
        return newArr
      }
      console.log(unique(arr))  // [1,2,3,4,5]
    </script>
  </body>
</html>
